Resource Calendar: Resource Calendar indicates the days, dates and time a particular resource (human resources/machines/etc.) will work.
In the PMP® Exam, Resource Calendar is mainly about Human Resources as it is mentioned in the Project Human Resource Management Knowledge Group.
This is because a particular resource may be required to work concurrently for several projects and its share of availability for a particular project is limited, or there are planned vacation for resources, etc.
Resource Calendar is included in the Staffing Management Plan (which is part of the Human Resource Management Plan)
Output of Acquire Project Team process — by updating the original Resource Calendar (which was created in Plan Human resource management) with the details of the team members which were acquired during Acquire Project Team process